Several publications and patent documents are cited throughout the specification in order to describe the state of the art to which this invention pertains. Each of these references is incorporated herein as though set forth in full.
Improved treatments for many childhood cancers provide hope of long term survival for these patients. In the year 2000, it was estimated that 1 in 900 people aged 15–44 in the United States were cancer survivors (Bleyer WA., CA Cancer J Clin 1990; 40: 355–367). However, often the treatments used have long term negative effects, such as decreased fertility. A large study of childhood cancer survivors treated between 1945 and 1975 showed an adjusted relative fertility of 85% compared with that of their siblings. The adjusted relative fertility of male survivors was slightly lower than that of female survivors. The most dramatic declines in relative fertility rates were in male survivors who had been treated with alkylating agents (Byrne J, et al. N Engl J Med 1987; 317: 1315–1321). In one study of male children treated with alkylating agents for a variety of sarcomas, researchers found that 60% of participants had no sperm production, 29% had reduced sperm production, and only 12% had normal sperm counts. Higher doses of chemotherapy corresponded to lower sperm counts and poor morphology. All the patients who had been treated prior to puberty had abnormalities in their semen (Kenney et al., Cancer 2001; 613–621).
Spermatogenesis is a continuous, highly organized process that generates virtually unlimited numbers of sperm during adulthood. Many complex aspects of testis function in humans and large animals have remained elusive due to the lack of suitable in vitro or in vivo models.
Recent advances have opened new avenues for the study and preservation of gonadal function (Gosden R, et al. Reproduction 2002; 123:3–11). In the female, cryopreservation and grafting of the whole ovary or strips of ovarian tissue showed promising results in experimental studies, and might soon become a clinically useful strategy (Snow M, et al. Science 2002; 297:2227–2229; Wang X, et al. Nature 2002; 415:385–387; Picton H M, et al. Br Med Bull 2000; 56:603–615). In males, the advent of germ cell transplantation in mice (Brinster R L, et al. Proc Natl Acad Sci USA 1994; 91:11303–11307; Brinster R L, et al. Proc Natl Acad Sci USA 1994; 91:11298–11302), domestic animals (Honaramooz A, et al. Biol Reprod 2002; 66:21–28; Honaramooz A, et al. Mol Reprod Dev 2003; 64:422–428), and primates (Schlatt S, et al. Hum Reprod 1998; 14:144–150; Schlatt S, et al. Hum Reprod 2002; 17:55–62), the in vitro culture of male germ cells (Tesarik J, et al. Lancet 1999; 353:555–556), and the generation of immortalized cell lines from the male germ cell lineage (van Pelt A M, et al. Endocrinology 2002; 143: 1845–1850; Feng L X, et al. Science 2002; 297:392–395; Cooke H J et al. Nat Genet 2002; 32:90–91) are innovative tools leading to rapid scientific progress but are still at an experimental stage (Schlatt S, et al. Endocr Dev 2003; 5:136–155). Transplantation of spermatogonial stem cells from fertile donor mice to the testes of infertile recipient mice resulted in complete spermatogenesis (Brinster, R. L. et al. (1994) Proc. Natl Acad. Sci. USA 91, 11303–11307; Jiang, F. X. et al. Int. J. Androl. (1995) 18, 326–330; Ogawa, T., et al. Nature Med. (2000) 6, 29–34) and autologous transplantation was successful in the monkey (Schlatt, S. et al. Hum. Reprod. (1998) 14, 144–150) opening the field for medical applications (Schlatt, S., et al. Brit. Med. Bull. (2000) 56, 577–587). Cross-species transplantation of spermatogonial stem cells recovered from donor rats or hamsters to recipient mice resulted in the establishment of rat or hamster spermatogenesis in the mouse testis (Ogawa, T., et al. Biol. Reprod. (1999) 60, 515–521). However, transplantation of germ cells from phylogenetically more distant species including rabbits, dogs, pigs, bulls, horses and primates, including humans, into mouse testes, did not result in spermatogenesis beyond the stage of spermatogonial proliferation (Dobrinski, I., et al. Mol. Reprod. Develop. (2000) 57, 270–279; Nagano, M., et al. Biol. Reprod. (2001) 64, 1409–1416; Russell, L. D. et al. in Histological and Histopathological Evaluation of the Testis (eds Russell, L. D., Ettlin, R. A., SinhaHikim, A. P. & Clegg, E. D.) 1–40 (Cache River Press, Clearwater, 1990); Nagano et al., Fertil. Steril. (2002) 78(6):1225–33) likely due to the incompatibility of microenvironments.
Therefore a need exists in the art for a method of preserving fertility in prepubescent males who require chemotherapy, and for providing an improved model for study of testicular development and function.